Goodwill and Other Intangible Assets (Schedule of intangible assets and goodwill) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Amortized intangible assets:
Gross carrying value	$ 66,724	$ 66,724
Accumulated amortization	(12,843)	(11,283)
Net carrying amount	53,881	55,441
Goodwill
Gross carrying value	168,311	166,796
Accumulated amortization
Net carrying amount	168,311	166,796
AEC Trade Names [Member]
Amortized intangible assets:
Gross carrying value	140	140
Accumulated amortization	(126)	(125)
Net carrying amount	$ 14	$ 15
Goodwill
Amortization life in years	15 years	15 years
AEC Technology [Member]
Amortized intangible assets:
Gross carrying value	$ 370	$ 370
Accumulated amortization	(296)	(290)
Net carrying amount	$ 74	$ 80
Goodwill
Amortization life in years	15 years	15 years
Customer Relationships [Member]
Amortized intangible assets:
Gross carrying value	$ 48,421	$ 48,421
Accumulated amortization	(6,462)	(5,654)
Net carrying amount	$ 41,959	$ 42,767
Goodwill
Amortization life in years	15 years	15 years
Customer Contracts [Member]
Amortized intangible assets:
Gross carrying value	$ 17,471	$ 17,471
Accumulated amortization	(5,830)	(5,102)
Net carrying amount	$ 11,641	$ 12,369
Goodwill
Amortization life in years	6 years	6 years
Other Intangible [Member]
Amortized intangible assets:
Gross carrying value	$ 322	$ 322
Accumulated amortization	(129)	(112)
Net carrying amount	$ 193	$ 210
Goodwill
Amortization life in years	5 years	5 years
MC Goodwill [Member]
Goodwill
Gross carrying value	$ 72,581	$ 71,066
Accumulated amortization
Net carrying amount	72,581	71,066
AEC Goodwill [Member]
Goodwill
Gross carrying value	95,730	95,730
Accumulated amortization
Net carrying amount	$ 95,730	$ 95,730